To Port or Not to Port - Stealth Fighter

Do you remember a time when owning a Mopar vehicle meant not being able to find economically-priced aftermarket parts to make your car or truck faster? We sure do, and if it weren’t for the fact that Mopars ran so good in stock form, we may have succumbed to the temptation to buy an off-brand car simply because there were an abundance of parts available. Things have changed however, and now is a good time to be a Mopar enthusiast. Mopars have come into style over the past couple of decades, and the aftermarket has responded with an abundance of go-fast goodies for Pentastar owners. There are literally thousands of parts available for just about every popular body style and engine, and prices for these parts have come down significantly.

When it comes to a car’s performance the engine is the first part that comes to mind for most of us, and Chrysler manufactured some of the best engines in the industry to power their muscle cars. Of all the engines produced by Chrysler, the big-block was the most widely installed in performance vehicles, and in terms of torque, horsepower, and reliability is one of the best choices for a Mopar. One area that is an Achilles heel of the 440, however, is the cylinder heads. Stock 440 heads just don’t allow enough flow for serious performance, and stock 440 heads are all made from cast-iron, making them heavy as well. Fortunately, 440 Source has an economical alternative to stock 440 heads with their Stealth line of aluminum replacements.

2/15It’s sometimes hard to believe that we can now get assembled aluminum cylinder heads for our big-blocks for less than a grand. This month we’ll install unported and ported Stealth heads on our dyno 440 and see how they stack up.

Aside from the other performance advantages, aluminum cylinder heads offer the distinct advantage of weighing some 40-50 pounds less than comparable cast-iron heads. The Stealth head also offers a closed chamber design for maximum quench area in the combustion chamber, and better intake and exhaust flow than any factory 440 cylinder head. The Stealth heads are also a direct replacement for the popular “906” casting factory head, are dimensionally the same, and utilize the same rocker gear and pushrods. These big-block heads are also, well, “stealthy” as they look identical to factory heads if painted. The best feature of the Stealth heads, however, has got to be the price. In stock, unported form, these heads come fully assembled with valves, springs good for a .600-inch lift flat-tappet camshaft, retainers, and locks for the surprisingly low price of $995 per pair.

With such a low price these heads are very cost effective, as you’d likely have this much (or more) money wrapped up in rebuilding factory heads by the time you installed stainless steel valves, new valve springs, and paid a machine shop to perform a valve job and replace any guides or seats that were excessively worn. To test the performance of the Stealth heads, we decided to bolt a pair of these on the 440 we built and dyno’d in the May 2012 issue, to see how well they compared to the 915 casting heads we already had on our big-block. The 915 heads offer a similar combustion chamber design, so compression ratios between the two heads will be very similar. While we’re at it, we’ll also bolt a pair of 440 Source’s CNC ported Stealth heads onto our engine, and let you know how much power we gain with a ported version. The CNC ported versions of these heads cost an extra thousand dollars, but for large displacement street or race engines this extra cost could be worth the money.

The 440 we’re using to test these heads is one we built on a budget in the April issue of Mopar Muscle. With a standard bore and stroke, just over 10.0:1 compression, Speed Pro forged pistons, and a Comp flat-tappet camshaft, this engine is typical of what many readers would build for their Mopar. The 915 heads on this engine are typical, built with a small amount of bowl cleanup, a multi-angle valve job, Comp valvesprings, and gasket matched intake and exhaust ports. These are not all-out "race-prepped” heads, just typical cleaned up and freshened factory castings. On the dyno at Auto Performance Engines (APE), this 440 made 460 horsepower and 466 lb-ft of torque using a Mopar Performance M1 intake and 950 cfm Holley Ultra HP carburetor, and once we bolted on a 1050 cfm Dominator, our 440 achieved a best pull of 467 horsepower and 469 lb-ft of torque. Using this pull as a baseline, we decided to bolt on our unported, out of the box Stealth aluminum cylinder heads and then a CNC ported set of Stealth heads to see how they compared.

Even without dyno gains, the Stealth cylinder heads have an advantage simply by being made from lightweight cast aluminum. Better yet, the weight savings is seen at the front of the car, where it matters most. Before bolting the heads on our 440, we ran all three sets of heads across the flow bench at APE. As expected, the mildly-worked factory 915 heads showed the least amount of flow, with the un-ported Stealth heads showing an improvement, and the ported Stealth heads showing the best flow at 323 cfm on the intake side and 271 cfm of exhaust flow.

On the dyno, the results showed exactly what the flow charts showed. By bolting on the “out of the box” Stealth heads and changing nothing else, our 440 street engine picked up power across the board, with peak horsepower climbing to 475 hp, and peak torque to 480 lb-ft. The average numbers of torque and horsepower were also up significantly, a clear indication that the $995 Stealth heads beat our factory 915 castings hands-down. Given that the 915 heads cost us $100 at a swap meet, and then were treated to a valve job, Comp springs, two valve seats, and all new guides, the Stealth heads become a better deal yet. Add stainless steel valves, the labor of port work, surfacing if needed, and the cost of our factory heads quickly not only meets, but exceeds the cost of the Stealth heads.

One area where the factory castings can’t compete at all is the weight of the heads. No matter how much porting and cutting you do to factory heads you can’t reduce their weight by the 40-50 pounds saved by using the aluminum Stealth heads. The other area where factory castings can’t compete is with the flow numbers seen by the CNC ported Stealth heads. It would be nearly impossible to get the same flow from any factory cylinder head that we saw with the CNC ported Stealth heads, and the number of hours it would take to achieve numbers even close to the CNC Stealth’s numbers would make the task cost prohibitive.

On the dyno, we had to utilize a different intake with the ported Stealth heads since the intake ports of the heads were taller than the runners of our M-1 intake manifold. To keep our comparison as close as possible, we utilized an Indy Cylinder Head single-plane aluminum intake we had on the shelf. This intake has approximately the same plenum volume as the M-1, with ports more closely matched to the ports of the ported Stealth heads. During our dyno session the CNC ported Stealth heads showed substantially more power than the unported versions on our relatively mild 440, and power numbers climbed to an impressive 532.1 horsepower and 483 lb-ft of torque. On a larger displacement or more race-oriented engine, we’re sure the ported heads would have shown even more sizeable gains.

We learned a lot from out test of 440 Source’s Stealth aluminum cylinder heads, and the results shown in the dyno sheets speak for themselves. Of course there are bigger, more exotic, and more expensive cylinder heads on the market for your big-block Mopar, but if you’re looking for a lightweight, economical upgrade to factory big-block cylinder heads we found 440 Source Stealth aluminum heads to be a great option. Look over our dyno sheets carefully, and we think you’ll agree that for the money, these heads are hard to beat. To see videos of our 440 making dyno pulls, be sure to log onto www.moparmuscle.com.

Price Tag

440 Source Aluminum Cylinder Heads

$995 assembled

440 Source Aluminum Cylinder Heads CNC Ported

$1995 assembled

915 Cast Iron Cylinder Heads

Cost varies by parts used, repairs and machine work needed, and port work